Known needles for suction and injection of medical substances, which needles have a flow direction which is substantially parallel to the longitudinal extension of the needle, i.e. the liquid flows out from or into the needle in a main direction which is substantially parallel to the longitudinal centre line of the needle, are primarily used for injection of pharmaceutical preparations into a patient or for drawing of blood from a patient. In such cases, the needle penetrates the skin and the tissues directly under the skin and there is a strong-felt desire that the penetration may be performed while causing as little pain as possible for the patient. For this reason, the needles are designed to require as small a force as possible when the skin is penetrated and this may be achieved by the needle being ground so that the penetrating tip of the needle has sharp edges which cut an incision in the skin, through which incision the needle is inserted into the body of the patient.
Traditionally, needles of the type discussed above are also used for penetrating a membrane when medical substances are handled. Such membranes are frequently used in medical systems, for example as a seal of a container, such as medicine bottles or similar. In this connection, the needle has two functions; the needle shall penetrate the membrane, and the needle shall transport the substance. However, these needles have important drawbacks due to the fact that sharp edges of the tip of the needle may release particles from the membrane. This effect is called “coring” and is primarily initiated from sharp inner edges of the lumen of the needle. A core from the membrane, made of rubber for instance, could be produced when the needle penetrates the membrane. These cores or particles may be carried by the needle and contaminate the substance transported via the needle. Further problems arise as a consequence of the fact that the needle leaves a cut in the membrane when the membrane is penetrated, which cut has an extension corresponding to substantially the width of the edge of the needle. One or more such cuts of the membrane may result in the membrane not being able to fit tightly around the needle and, thus, leakage may arise. When medical substances are handled, it is often an absolute condition that leakage does not arise, since in the case of a leakage, the substance may be contaminated and/or spread to the environment. Furthermore, after several penetrations, parts of the membrane may be released, i.e. may be cut away, from the membrane and contaminate the current substance.
Some known needles have been developed taking into account the aspect of avoiding coring from a sharp inner edge of the lumen of the needle by mechanical blasting treatment thereof. However, since the needle must have a sharp outer edge on the tip of the needle to obtain good penetration properties as discussed above, and the needles are mass-produced, the needles are manufactured to obtain the best penetration and cutting properties at the expense of the anti-coring properties, i.e. it is not possible to blast the outermost part of the tip because in that case the cutting properties of the needle are impaired.